Remove CI build for Portenta H7 / M4 core (#34)

The reason behind this is that the M4 core can not access memory area that's relevant for the Ethernet driver. Put simply, Ethernet does not work from the Portenta H7 / M4 core.

Author: aentinger

.github/workflows/compile-examples.yml

@@ -76,11 +76,6 @@ jobs:
               - name: arduino:samd
             type: ethernet
             artifact-name-suffix: arduino-samd-nano_33_iot
-          - fqbn: arduino:mbed_portenta:envie_m7:target_core=cm4
-            platforms: |
-              - name: arduino:mbed_portenta
-            type: ethernet
-            artifact-name-suffix: arduino-mbed_portenta-envie_m7-cm4
           - fqbn: arduino:mbed_portenta:envie_m7
             platforms: |
               - name: arduino:mbed_portenta